It has long been the practice in automobile, and other automotive equipment, engines to control knock (premature or erratic ignition of a fuel charge in a combustion chamber) by using properly rated anti-knock fuels such as those containing tetraethyl lead or other so-called "knock improvers." Alternatively (or additionally), spark ignition engines have long controlled advance or retard of spark in response to intake manifold pressure to control or suppress potential knocking. In such systems, a rise in intake manifold pressure causes the spark to retard automatically. In general, maximum knock occurs only during a small percent of time that the engine is operating, for example, when climate (heat or humidity) or driving conditions, (grade or acceleration), apply a heavy load to the engine. Accordingly, highly treated or refined, (and hence expensive) fuels to satisfy normal, knock-free operation of the engine, are not necessary over most normal operating conditions. Additionally, usual spark retardation systems are generally dependent on high manifold pressure, which may or may not be associated with potential knocking conditions for the engine. In general, spark retardation robs the engine of power and can result in excess consumption of fuel.
It has been proposed, but never adopted commercially on a large scale, to use two separate sources of fuel to provide knock-free operation of an internal combustion engine. It has also been proposed to use a knock sensor or detector to switch fuel supply from a normally low knock-rated fuel to a higher knock-rated fuel. A primary difficulty with such a system is that on presently existing automobiles, retrofitting of another fuel tank is difficult because of limited space. Also, on new vehicles it would be expensive. Further, in normal operation, the operator would need to find a proper balance between the amount of low knock-rated fuel and high knock-rated fuel to use in such a system.
Alternatively, systems have been disclosed which employ a knock sensor, such as a magnetostrictive device of the type disclosed in Pat. No. 2,445,318, located on one of the combustion chambers of the internal combustion engine, to control automatically spark retardation. The retard command may be proportional to the intensity of the knock present in the engine, and in response thereto ignition pulses are delayed either mechanically or electrically from the distributor to each spark plug. This requires use of a spark distributor able to accept such a delay. Upon reduction in detected knock, a controller restores the distributor spark to its normally advanced position. A description of the latter system is given in an article entitled, "Energy Conservation With Increased Compression Ratio and Electronic Knock Control" by James H. Currie, David S. Grossman, and James J. Gumbelton, published by the Society of Automotive Engineers, Inc., Paper No. 790173. Description of a system for using two fuel systems under the control of a knock sensor is disclosed in a paper published by A. T. Colwell and Thompson Vitameter Corporation, dated Nov. 11, 1947, entitled, "A Program for Anti-Detonant Injection as Applied to Petroleum and Automotive Industries".
McNally, Pat. No. 2,958,317 discloses an anti-detonant system for internal combustion engines in which a knock detector is used for controlling introduction of anti-knock additive either directly into the liquid fuel line or as an aerosol spray into the fuel-air system of the intake manifold. The amount of anti-knock additive is introduced as pulses "shots" of given quantity or so long as knocking is detected. The amount of anti-knock additive introduced may be controlled in response to the extent of knock detected. However, there is no system for modulating or regulating the amount of anti-knock additive in relation to actual engine load condition causing engine knock. I have found that when constant volume pulses are added over the entire engine speed range, say from 600 to 4,000 RPM, the amount of such anti-knock additive is either excessive or inadequate. Where excessive, a small supply, say a quart or two, of such additive to 15 gallons of regular low knock-rated fluid may be quickly exhausted. If inadequate, knock will persist even when pulses of anti-knock fluid are being added to the engine fuel supply. Accordingly, the consumption of anti-knock additive is relatively high and generally unsatisfactory for any detected knock in the engine, and in particular, where knock is only sporadic or intermittent.
Whitty et al, Pat. No. 2,403,774, shows a system for introducing water as an anti-knock suppressant in response to knock or detonation in the engine. It likewise does not show any system for controlling the amount or duration of the anti-knock suppressant apart from detected knock itself.
Van Dijck et al, Pat. No. 2,220,558, discloses a knock suppressing system, which in response to knock alone, modifies the fuel-air ratio, or anti-knock additive supplied to the fuel-air mixture, or retards the spark ignition temporarily.
Other methods have been disclosed for adding anti-knock fluids to the intake system for an internal combustion engine based upon measurement of other conditions. For example, Von Brimer, Pat. No. 3,530,842, introduces anti-knock fluid in accordance with the rate of exhaust gas recirculation to reduce any tendency of an engine to knock, but without actual measurement of knock in the engine. Spears, Pat. No. 4,096,829, injects an anti-knock suppressing fluid, such as water, in response to engine spark ignition rate, representative of engine speed.
Alquist Pat. No. 3,120,218, discloses a system for varying the fuel-air ratio and addition of knock suppressing fuel, such as liquefied petroleum gas or natural gas, in response to outside air conditions, primarily temperature.
Kimball, Pat. No. 2,023,892, discloses mechanical means for retarding spark advance dependent upon engine RPM and carburetor throttle-valve opening.